1. Field of the Invention
The present invention relates to a process for producing C1-C4 alkyl nitrite, in particular a process for producing C1-C4 alkyl nitrite by reaction in a rotating high-gravity reactor, wherein C1-C4 alkyl nitrite is useful in the production of oxalate by CO coupling.
2. Description of the Related Art
Oxalate is an important organic chemical material, and widely used in fine chemicals for the production of various dyes, medicines, important solvents, extractants and intermediates. In 21st century, oxalate as a degradable environmental-protection-type engineering plastic monomer is internationally and widely recognized. In addition, hydrolysis of oxalate at normal pressure can produce oxalic acid, and aminolysis of oxalate at normal pressure can produce high grade sustained-release fertilizer—oxamide. Oxalate can also be used as solvent for production of medicines, dye intermediates and the like. For example, various condensation reactions can be carried out by using oxalate together with fatty acid esters, cyclohexylacetophenone, amino alcohols and many heterocyclic compounds. Oxalate can also be used for synthesizing thymine as hormone in the medicine. Low pressure hydrogenation of oxalate can be used for producing ethylene glycol which is a very important chemical raw material. Currently, ethylene glycol is heavily dependent on production via the petroleum routine and has a higher cost. China imports a lot of ethylene glycol each year, and the import volume in 2007 was close to 4,800,000 tons.
The conventional process for production of oxalate involves preparing by esterification of oxalic acid with alcohols, which has a high production process cost, high energy consumption, heavy pollution and unreasonable utilization of raw materials. People are seeking for a low cost and environment-friendly process route. In the 1960s, D. F. Fenton of Integrated Oil Company, U.S.A. found that dialkyl oxalate could be directly synthesized from CO, alcohols and oxygen by oxidization-carbonylation. From then on, UBE Industries Ltd., Japan and ARCO, U.S.A. successively carried on studies and developments in such field.
As seen from the development course, the synthesis of oxalate by the CO oxidization-coupling method can be divided into the liquid phase method and the gaseous phase method. The synthesis of oxalate by the CO liquid phase method requires more stringent conditions: the reaction is conducted at high pressure; the apparatus is easily corroded by the liquid phase system; and the catalyst is easy to lose during the reaction. The gaseous phase method for producing oxalate by CO coupling is advantageous. Sequentially, UBE Industries Ltd., Japan and Montedison S.P.A, Italy have also developed studies on the gaseous phase method in 1978, wherein the process for synthesizing oxalate by gaseous catalysis developed by UBE Industries Ltd. is conducted at a pressure of 0.5 MPa and a temperature of 80-150° C.
The reaction procedures for synthesizing oxalate are as follows.Coupling reaction: 2CO+2RONO→2NO+(COOR)2  (1)Regeneration reaction: 2ROH+0.5O2+2NO→2RONO+H2O  (2)
According to the procedures above, it can be seen that the technical key of such system lies in reasonably utilizing NO, RONO, ROH in said two-step reaction procedures in high selectivity and high efficiency.
However, the truth is that, except for the primary product-alkyl nitrites, side reactions, in particular production of side product-nitric acid, often occur in the reaction procedure of step (2), which necessarily consumes more NO gas, increases energy consumption and cost and erodes the apparatus at the same time. Although there are many documents regarding how to produce alkyl nitrites, there is less report on how to effectively increase selectivity of alkyl nitrites, and to prevent in a better way the side reaction of nitric acid from occurrence.
CN200710060003.4 discloses a process for preparing diethyl oxalate by CO coupling, comprising using the gaseous phase method, coupling CO by catalyzing with a bi-metal supported-type catalyst in the presence of ethyl nitrite to produce a crude product of diethyl oxalate. The reaction is a self-sealing circulation process. CO gas is mixed with ethyl nitrite from the regeneration reactor, preheated and fed into a coupling reactor. After reaction, the gas is condensed and separated to obtain a colorless, transparent condensate of diethyl oxalate. Uncondensed gas containing NO is re-fed into the regeneration reactor to react with ethanol and oxygen and to produce ethyl nitrite, and the resultant ethyl nitrite is recycled to the coupling reactor for continuous use. The selectivity of ethyl nitrite is not mentioned in the invention.
CN 95116136.9 discloses a catalyst for synthesizing oxalate, wherein Zr is used as an auxiliary agent for developing a novel Pd—Zr/Al2O3 catalyst by the immersion method. Such catalyst is used for synthesizing oxalate from CO and nitrite via gaseous phase catalysis in a fixed bed reaction apparatus. Likewise, such patent document does not involve the selectivity of nitrites and the inhibition against the side reaction of nitric acid.
Hypergravity technology is the new technology strengthening the multiphase flow transmission and reaction process, and widely recognized at home and abroad since it came out in the last century. It has a widely commercial application prospect in the industrial fields of environmental protection and material biological chemistry. However, hypergravity technology is at an application-developing stage at present. Moreover, no study on the application of the rotating high-gravity reactor in the production of C1-C4 alkyl nitrite has been reported.